1. Field of the Invention
The present invention relates to a device for terminating a fusible element of an interrupting module and, more particularly, to a device to which the respective ends of a fusible element of an interrupting module may be electrically and mechanically connected, the device also supporting insulative notched fins about which the fusible element is helically wound, so that the fusible element is connected in electrical shunt with a switch, also contained in the module. The present invention constitutes an improvement of the interrupting modules discloses in commonly assigned co-pending U.S. patent applications, Ser. Nos. 437,925 filed Nov. 1, 1982, now U.S. Pat. No. 4,227,963, issued Jan. 24, 1984, 437,926 filed Nov. 1, 1982, 439,443 filed Nov. 5. 1982, now U.S. Pat. No. 4,434,415, issued Feb. 28, 1984, all in the names of Jarosz and Panas; Ser. No. 188,660, filed Sept. 19, 1980, now U.S. Pat. No. 4,370,531 in the name of Tobin; Ser. No. 179,367, filed Aug. 18, 1980 now abandoned, and Ser. No. 181,603, filed Aug. 27, 1980, now abandoned, both in the names of Jarosz and Panas; Ser. No. 179,366, filed Aug. 18, 1980 now abandoned, in the name of O'Leary; and in commonly assigned U.S. Pat. No. 4,342,978 issued Aug. 3, 1982 in the name of Meister. Further, the device of the present invention may conveniently be used with any fusible usable in a current-limiting fuse, including the fusible elements disclosed in commonly assigned U.S. Pat. No. 4,359,708 issued Nov. 16, 1982, and in commonly assigned U.S. patent application, Ser. No. 437,776 filed Oct. 29, 1982, both in the names of Jarosz and Panas.
2. Discussion of the Prior Art
U.S. Pat. No. 4,342,978 discloses and claims an interrupting module of a current-limiting fuse having a high continuous current rating. The interrupting module comprises a more or less typical current-limiting section, which includes a helically wound fusible element embedded in a compacted mass of a fulgurite-forming medium, such as silica-sand. An outer insulative housing is filled with the sand and surrounds the fusible element. Also within the outer housing is a normally closed switch. The switch includes a pair of contacts which are relatively movable apart along a fixed line of direction for opening thereof. Each end of the fusible element is respectively electrically connected to one of the contacts, which are, in turn, electrically continuous with end terminals carried by the outer housing and by which the module is connected to a high-voltage electrical circuit for protection thereof. The fusible element is maintained in its helical configuration by a pair of notched fins or beams, preferably made of mica, which are positioned diametrically opposite each other along an inner insulative housing also surrounding the switch. Preferably, the inner housing is within and coaxial with the outer housing. Opposed ends of the inner housing are carried by the end terminals.
The impedance of the electrical path through the switch is substantially less than the impedance of the path through the fusible element so that, with the switch normally closed and with the module connected to the protected circuit, the majority of the current in the protected circuit flows through the switch, and not through the fusible element. When a fault current, or other over-current, is detected by sensing facilities, a power cartridge is ignited. Ignition of the power cartridge pressurizes a chamber defined by one of the contacts and by a trailer or piston carried by the other contact, which is movable away from the one contact.
The increase in pressure within the chamber caused by ignition of the power cartridge rapidly moves the trailer and the movable contact carrying it away from the one contact to open the switch, thereby rapidly commutating the fault current in the switch to the fusible element, which interrupts the current in a more or less typical fashion. During movement apart of the contacts, the trailer isolates the widening gap between the contacts and the movable contact from the ignition products of the power cartridge which may be conductive. This isolation inhibits or prevents arcing between the separating contacts. Further, in the event any arc does form between the contacts, the trailer moves through a bore within, and co-acts with, an insulative tube or liner for constricting such arc. The trailer and the tube may, if necessary, be made of an arc-extinguishing material which, when subjected to the high heat of an electrical arc, evolves large quantities of cooling, de-ionizing, and turbulent gases, which along with arc constriction are effective to extinguish any arc which forms.
It has been determined to be desirable to provide a simple, inexpensive device for terminating the fusible element of the interrupting module. Specifically, it has been determined to be desirable to provide a device to which the ends of the fusible element may conveniently and easily be connected, and which electrically connects the fusible element in shunt with the switch and which supports and locks in place the mica fins or beams which helically support the fusible element. The provision of such apparatus is a major object of the present invention.